The clamp yoke on a steering column or I-shaft of a motor vehicle is intended to transmit the steering torque to the pinion for the life of the vehicle, and without lash. These requirements can be problematic, especially in the case where electric power steering is used, and where the connection with the pinion is by serrations. Design limitations include bolt tightening torque (limited by material characteristics and the need to avoid thread stripping); and minimum/maximum lash between the yoke and pinion (the minimum lash has to guarantee the assembly and so the maximum lash is given by minimum lash plus feasible tolerances for yoke and pinion interface). The worst case is given by the lower limit of bolt tightening torque and the upper limit of the lash between the yoke and the pinion. In this condition there is a need to improve at the maximum the elasticity of the yoke to be able to lose or reduce the minimum of the tightening torque to deform the yoke (have the higher portion of tightening torque that is transformed in pressure between yoke and pinion). This clamping efficiency helps to withstand high torque peaks that can especially occur with electric power steering systems.
FIGS. 1 through 4 illustrate known arrangements for trying to overcome the above mentioned problems. Each of these illustrated arrangements show a clamp yoke 10 having a substantially U-shaped profile and including a base portion 12 and a pair of ear portions 14, 16. Axially aligned holes 18 are formed in the ear portions 14, 16. A serrated aperture 20 is formed in the base portion 12. A bolt hole 22 is formed in the base portion 12 adjacent the aperture 20. A slot 24 is cut from one end 26 of the base portion 12 to extend through the bolt hole 22 and open into the aperture 20. In FIG. 1, an additional hole 28 is drilled in one ear portion 14 of the yoke 10 at the end of the slot 24 to move the “hinge” as far as possible from the bolt hole 22. The elasticity of the yoke 10 on the other end 30 of the base portion 12 to the bolt hole 22 is improved, as shown in FIG. 2, by producing an asymmetric yoke 10 by reducing the amount of material on the other end 30 of the base portion 12. As an alternative, the elasticity of the yoke 10 is improved by drilling an axial hole 32 in the base portion 12 on the opposite side of the aperture 20 to the bolt hole 22, and then ensuring that the axial hole 32 opens through opening 34 into the aperture 20 during a subsequent broaching operation, as shown in FIGS. 3 and 4.
An example of the prior art is shown in FR-A-2857888.